Increasing fire emissions driven by warming

In the context of global climate change, the Arctic and boreal regions are warming at a rate much faster than the global average,  creating conducive conditions for wildfires including (but not limited to) extended fire season lengths, more extreme fire weather, increased fuel flammability, and more lightning ignitions. As a result, the frequency and intensity of wildfires in these regions have surged in recent years (Fig. 1b).  Our analysis shows that fire emissions have risen sharply over the past two decades in close correlation with warming, following an exponential relationship.  This suggests even small temperature rise would result in large emission spikes. The observed emission peak in 2019 during our study period is a good example of this non-linear relationship, with a threefold increase in emissions corresponding to a summer temperature anomaly of +1.3°C compared to the 2000-2020 average.

Satellite-constrained modelling suggests different climate impacts

With satellite-constrained modelling, we further evaluate how the Arctic climate responds to aerosols emitted from current and future fire activities. Prior modelling studies predominantly suggest fire aerosols are cooling agents in the Arctic, and our research challenges this perspective. By employing satellite constraints to enhance the reliability of modelled aerosol dynamics, we demonstrate that fire aerosols are contributing to the warming of the Arctic summer climate. This warming is primarily attributed to aerosol solar absorption (e.g., by black carbon) enhanced by bright sea surface with sea ice and low-level clouds (Fig. 2) and has been validated through independent observations, marking a significant advancement in understanding the role of fire aerosols in the Arctic climate.

Fire aerosols over the Arctic in a warming future

We not only look at the current dynamics but also provide a quantitative estimate of future boreal fire emissions. Based on the relationship between emissions and temperature of the past decades, boreal fire emissions are projected to increase sixfold per degree of global warming. These fire emissions would amplify Arctic warming by 35% compared to current CMIP6 estimates. Moreover, the future fire aerosols could completely offset the benefit (cooling) from an ambitious mitigation of anthropogenic black carbon emissions across the world as estimated by another study. This highlights the sizable impacts of fire aerosols—a crucial insight so far overlooked in current climate assessments.

Thoughts and implications

As boreal fires become more frequent alongside climate change, the escalating threat of boreal fires has caused widespread public concern. This work underscores that, beyond the greenhouse gases released by these fires, the impact of aerosols demands greater attention. This would contribute to more accurate climate assessments and effective mitigation policies.